Rockfish with Plum Sauce

Claudia Roden, in her iconic book on Jewish food, refers to a recipe of the Turkish Jews, eaten on a Friday night, that she describes as rockfish with plum sauce. However, she doesn’t give a recipe because she was not happy with the result. I was always intrigued by this and on finding a jar of umeboshi paste (made from pickled plums) in Waitrose, I decided to have a go with hake. So this is my variant, which